1. Field of the Invention
The present invention relates to a manufacturing method for a laminated chip electronic part, and more specifically to a manufacturing method for a laminated chip electronic part that permits the easy formation of external terminal electrodes on end surfaces only together with internal conductors.
2. Description of the Prior Art
There has been demand in the recent years for laminated chip electronic parts configured to be more compact and have higher performance than the conventional ones.
For laminated chip capacitors, for example, it is necessary to use a material with a higher dielectric constant and sheets that are thinner, but at the current stage it seems that there are limitations both to the raising of the dielectric constant of the material and to the thinning of sheets to be used for manufacturing the laminated chip capacitors.
Accordingly, a vertical laminated type chip capacitor has been proposed that has a structure that is different from the conventional structure (hereinafter referred to as the horizontal laminated type).
A conventional horizontal laminated type chip capacitor 20 is composed, as illustrated in FIG. 2 showing a side sectional view thereof, of an elementary body 23 formed by laminating insulating material sheets 22 having internal electrodes 21 formed on the surfaces thereof and a pair of external terminal electrodes 24 formed at both ends of the elementary body 23 so as to be conductively connected alternatively to the internal electrodes 21. Here, the surfaces of the internal electrodes 21 are nearly perpendicular to the end surfaces of the external electrodes 24.
In contrast, a vertical laminated chip type capacitor 30 uses an elementary body 34 formed by laminating insulating material sheets 33 which have internal electrodes 31 formed on the surfaces thereof and via holes 32 as illustrated in FIG. 3 showing a plan sectional view of the chip capacitor 30. Furthermore, a pair of external terminal electrodes 35 are coated or formed at both ends in the laminating direction, or the uppermost end and lowermost end.
The internal electrodes 31 are conductively connected alternately to one another by way of the via holes 32. The internal electrode 31 of the uppermost layer is conductively connected to one of the external electrodes 35 by way of the via hole 32, whereas the internal electrode 31 of a lowermost layer is conductively connected to the other external electrode 35 by way of the via hole 32. In this case, the surfaces of the internal electrodes 31 are nearly in parallel with the end surfaces of the external terminal electrodes 35.
The former ordinary structure (horizontal laminated type of FIG. 2) requires that a margin of at least 50 .mu.m be reserved from the internal electrodes 21 to six surfaces of the elementary body 23, thereby limiting the obtainable maximum capacity in of itself when the elementary body 23 has a fixed size.
In contrast, the latter vertical laminated type of FIG. 3 permits formation of the internal electrodes 31 even in the vicinities of the end surfaces of the external terminal electrodes 35, thereby making it possible to obtain a maximum capacity which is larger than that of the horizontal laminated type when the elementary bodies have the same size.
In recent years, the need, for high-frequency parts has been increasing, and, laminated inductors with higher resonance frequencies (f.sub.0) have been in demand.
Furthermore, it has been required or indispensable to discriminate between such high-frequency parts with markers, since mounting characteristics such as resonance frequencies vary depending on asymmetries of the parts.
Speaking concretely, a conventional horizontal laminated type chip inductor 40 is composed, as illustrated in FIG. 4 (a side sectional view thereof), of an elementary body 43 which is formed by laminating insulating material sheets 42 with internal conductors 41 and via holes formed on surfaces thereof so that the internal conductors 41 are conductively connected spirally by way of the via holes, and a pair of external terminal electrodes 44 are formed at both ends of the elementary body 43 so as to be conductively connected to both ends of a coil conductor including the spirally connected internal conductors 41.
In this case, the surfaces of the internal conductors 41 are nearly perpendicular to the end surfaces of the external electrodes 44. Furthermore, high-frequency parts mounted on conductive pattern of printed circuit boards, the produce different influences on the internal conductors 41 between for the cases in which the surfaces of the internal conductors 41 are (1) parallel to the printed circuit board and (2) perpendicular to the circuit board, thereby differentiating the characteristics of the high-frequency parts. Accordingly, it is necessary to print marks on the parts themselves to recognize the direction of the surfaces of the internal electrodes.
When the markers are printed on the parts themselves, however, it is necessary to check the markers to discriminate directions in the taping and mounting stages, thereby causing inconveniences such as a remarkable lowering of productivity.
As a result, parts which have no directivity and can cope with high frequencies are demanded in the market. As structures that meet these requirements, there are known structures (longitudinal laminated type) in which internal electrode patterns are formed in directions parallel to the end surfaces of external electrodes (Japanese Patents Application Laid-Open Nos. H8-55726, H9-129447 and so on).
A vertical laminated type chip inductor 50 is composed, as illustrated in FIG. 5 showing (a plan sectional view thereof) of an elementary body 53 that is formed by laminating insulating material sheets 52 having internal conductors 51 formed on the surfaces thereof and via holes, and a pair of external terminal electrodes 54 that are coated or formed at both ends in the laminating direction.
The internal conductors 51 are conductively connected spirally by way of the via holes, thereby forming a coil conductor both ends of which are conductively connected to the external terminal electrodes 54 respectively by way of the via holes. In this case, the surfaces of the internal conductors 51 are nearly parallel to end surfaces of the external terminal electrodes 54.
Since vertical laminated chip inductor 50 always has the surfaces of the internal conductors 51 perpendicular to a printed circuit board at the stage of mounting high-frequency parts on the printed circuit board, it does not allow influences due to conductive patterns on the printed circuit board to vary depending on the mounting conditions on the printed circuit board or the like, thereby not differentiating the characteristics of such high-frequency parts.
However, the conventional vertical laminated type chip capacitor described above (see FIG. 3) has external terminal electrodes 35 that are formed on the end surfaces and four side surfaces in the vicinity of the end surfaces of the elementary body 34, which allows the external terminal electrode 35 formed on the side surfaces of the elementary body 34 to overlap the internal electrodes 31 on the side of the other electrode, thereby producing a floating capacitance between the external terminal electrode 35 and the internal electrodes 31. Accordingly, this vertical laminated type chip capacitor poses a problem in that it reduces the correlation between a number of the internal electrodes 31 and an actually obtained capacity value, thereby making it hard to design a capacitor having a precise desired capacitance value.
On the other hand, the conventional vertical laminated type chip inductor described above (see FIG. 5) poses, like the capacitor described above, a problem in that it has a floating capacitance between the internal conductors 51 and the external terminal electrodes 54, depending on the size of the external terminal electrodes 54, thereby lowering the resonance frequency (f.sub.0).
In order to solve these problems, there has been considered a method of coating the external terminal electrodes 35 or 54 only on the end surfaces of the elementary body 34 or 53, except for the side surfaces thereof. However, this method requires setting of an external electrode coating machine under delicate conditions, thereby tending to allow voids to be formed between the elementary body 34 or 53 and the external terminal electrodes 35 or 54 coated thereto. Further, this method involves a problem in that it is difficult to ensure a high bond strength between the elementary body 34 or 53 and the external terminal electrodes 35 or 54, thereby making it difficult to perform stable coating of external electrodes.
Furthermore, this method allows external electrodes to be formed only by coating a conductive paste onto a calcined laminated chip with a terminator or the like and drying or baking the paste. Accordingly, this method prolongs the process lead time in manufacturing of a laminated chip electronic part. This fact applies also to capacitors that have general horizontal laminated structures.